Vacuum distillation



Nov. 21, 1950 F. J. CASTLE ETAL VACUUM DISTILLATION Filed Feb. 27, 19483mm R. E.BEAL

F. J.CA$TLE %1 a 2} Patented'Ncv. 21,

VACUUM DISTILLATXON Francis J. Castle and Robert E. Beal, Peoria, 111.,

assignors to United States of America as represented by the Secretary ofAgriculture Application February 27, 1948, Serial No. 11.763

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) 4 Claims.

This application is made under the act of March 3, 1883, as amended bythe act of April 30, 1928, and the invention herein described, ifpatented in any country, may be manufactured and used by or for theGovernment of the United States of America throughout the world forgovernmental purposes without the payment to us of any royalty thereon.

This invention deals with a novel method for effecting low pressureevaporation and an apparatus therefor.

More particularly, the invention deals with vacuum distillation 'inwhich a film of liquid is caused to move adjacent to a relatively coolcon- (lensing surface in a rarified atmosphere. The film and thecondensing surfaces are separated by substantially unobstructed space,the film being heated by contact with an evaporation surface.

An object of this invention is to provide an improved method andapparatus for effecting vacuum distillation whereby the efficiency ofthe process is increased and the cost of the process is considerablydecreased.

Another object of the invention is to provide a novel and advantageousmeans for distributing the film of distilland over an evaporationsurface in vacuum stills.

In the past, vacuum stills have been provided with central members, suchas domes or columns. over which the distiland descends. Other stillshave been employed in which the distilland is caused to move over. aflat evaporation surface adjacent to a flat condensation surface. Theseprior columns or surfaces of other configuration are usually made ofglass or of some inert material presenting a relatively smooth surface,over which the distilland flows and from which vapors of the distillatemay leave to condense upon the condensation surfaces. These evaporationsurfaces are of varying shape and size, one of the simplest being theouter surface of a hollow cyinder.

In order to increase the sojourn of the distilland and to preventchanneling, it has been proposed to provide the surfaces of evaporation,such as a column, with a glass coil or to fabricate it in such a manneras to provide a winding or tenuous path for the distilland. It has beenfurevaporation surface.

2 interrupted bands or a helically wound strip of metal gauze.

These prior devices and methods are attended by many disadvantages.Residues of a gummy or tarry nature tend to accumulate upon the Anyroughening or unevenness of the surface, such as are caused by groovesand the like, make the surface extremely difficult to clean. Distillandsvary in their surface and flow characteristics and any one particularsurface is not universally satisfactory. Special fabrication orsurfacing increases the cost materially and in the majority of casesreduces the strength of the apparatus. Bands or strips of metal gauzepermit fouling of the evaporation surface in the exposed portions, andthe distilland tends to accumulate a small but neverthelessobjectionable amount of metallic ions from the gauze. In the case ofedible oils this metal content hastens flavor deterioration of the oil.The gummy or tarry residue which accumulates on the gauze requiresdrastic solvent action for removal, which tends to attack the gauzeitself.

According to this invention, the evaporation surface is fabricated of arelatively smooth and strong material and over this surface is placed aflexible and pliable substantially complete yet permeable covering ofinert material, such as fiberglass cloth, which serves to distribute thedistilland and to retain substantially all tarry or gummy residue.

This covering substantially prevents the surface itself from collectingresidue material and the still is therefore extremely easy to keepclean. In the usual high vacuum still the inert distributing materialmay be installed merely by drawing a mesh tube or sleeve of fiberglassor asbestos cloth over the column. The still may be substantiallycleared of the fouling matter by merely removing and ceaning thecovering sleeve. This sleeve is easy to remove and may be cleaned byimmersing or washing in a cleaning medium. The cost is relatively verylow compared with the special means of distributing the distilland overthe evaporation surface used in the past.

The use of a permeable covering in accordance with this inventionaccomplishes efiicient distribution of the distilland over theevaporating surface without weakening it or introducing foreign materialinto the distilland. Moreover, a distinct advantage gained by the use offiber glass or asbestos cloth is the inertness of the material 9 5h;very strong acid cleaningsolutions which are usually necessary to removeaccumulated residues.

Another advantage of our invention is the fact that the capacity of anyparticular still may be varied between wide limits by varying thespecific type of liquid distributor placed upon the evaporation surface.For instance, it may vary from a relatively thin coarsely woven mesh toa relatively thick retentive covering.

For a clearer understanding of the invention, reference is made to theaccompanying drawing.

Figure 1 is a vertical view, partly in section, of one form of theinvention;

Figure 2 is a cross-section of Figure 1 on line 2-2;

Figure 3 is a vertical view of a modified form of the covering,employing a spirally wound fiber glass or asbestos thread.

Figure 4 illustrates another modification, comprising a spirally woundstrip of fiber glass gauze.

Figure 1 illustrates a high vacuum still consisting of a tubularcondensing surface 4 inside which is disposed a vaporizing surface 5.Distilland enters through feed inlet I and is fed upon the evaporatingsurface which is heated internally by means of electrical resistanceunit 3.

The evaporation surface is covered by a liquid distributor 6 consistingofa mesh sleeve of woven fiber glass which distributes the distillandevenly as it descends over the evaporation surface. The uncondensedvapors are drawn off through outlet 2 while the condensed vapors collecton surface 4 and drain into distillate receiver 1. The undistilledresidue collects in receiver 8.

While fiber glass cloth is preferred as the material for fashioning thetube or seamless sleeve 6 because of its inertness, flexibility,durability, and ease of removal, we may also use asbestos cloth.

In place of the sleeve 6 we may use a spirally wound thread I I of glassor asbestos, as indicated in Figure 3.

In Figure 4 is shown a spirally wound gauze strip l woven of glass orasbestos thread. The adjacent turns of the strip overlap or are closelycontiguous, to cover the evaporating surface 5.

Strip I0 and thread I I may be removably fastened in place by anyconventional means, such as fastening clamps or rings.

The evaporation surface has been illustrated in one of its simplerforms, such as that of a vertical cylinder. It may also be a verticalseries of bulbous members. The column may be corrugated vertically orhorizontally. It may be an upright or inverted truncatoconical orconical member, or it may be a plane surface. The surface may be fixedrelative to the condensing surface, or it may be rotatable.

The means for supplying heat to the evaporation surface may be any ofthe usual means, such as liquid boiling under refiux, heat exchangefluid under circulation, and the like.

The apparatus and process of this invention are not limited to highvacuum distillation but may be applied to any process for distilling inwhich a materially reduced pressure is used. However, it is particularlyadvantageous in connection with the molecular distillation where thepressure is .01 mm. of mercury or lower and has been found to giveexcellent results in removing odorous constituents from vegetable oils.

In high vacuum or molecular distillation the pressure and the distancebetween the conden ing 4 surface and the surface of the distillandshould vary in inverse proportion to each other. In general, due topractical difficulties, the condensing surface should not be more thanone inch from the film of distilland.

Due to the flexibility and pliability of the m terial used to cover theevaporation surfacek may easily be made to conform to the shape 0 thatsurface. When the distributor becomes fouled or when a distilland of adifferent character is to be distilled, the distributor is simplyremoved and cleaned or a fresh one substituted.

Having thus described our invention, we claim:

1. A still comprising in combination a condensing surface and a tubular,smooth, heated evaporation surface spaced from the condensing surface,said evaporation surface having tightly fitted thereon a readilyremovable, flexible, pliable, and permeable covering sleeve of inert,acid-resistant, non-metallic, mesh fabric of mineral matter, todistribute the distilland supplied to the heated evaporation surface andto retain substantially all tarry and gummy residue formed at theevaporation surface and thus prevent the evaporation surface itself fromcollecting the said residue material, and means to supply distilland tothe heated evaporation surface.

2. In a short-path high vacuum still having a tubular distillandevaporating surface and heating means for said surface, and also havinga condensing surface; the improvement comprising a fiexible, detachable,pliable, inert, nonmetallic, covering tubular sleeve of fiber glass meshfabric fitting upon and in contact with and substantially coextensivewith the said heated evaporating surface, to distribute distillandsupplied to the heated evaporation surface and to retain substantiallyall tarry and gummy residue formed at the evaporation surface and thusprevent the evaporation surface itself from collecting the said residuematerial and means to supply distilland to the heated distillingsurface.

3. The apparatus of claim 1 in which the sleeve is made of woven fiberglass cloth.

4. The apparatus of claim 1 in which the sleeve is made of asbestosfiber cloth.

, FRANCIS J. CASTLE.

ROBERT E. BEAL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Fenske et al., Packing Material for FractionatingColumns, Ind. and Eng. Chem., Nov. 1944, pp. 1169-1177.

Minard et al., "Fibrous Glass Used in Packing Alcohol Columns, Chem. andMet. Eng, Feb. 1944, pp. 144446.

Stewart, Construction of Glass Helices for Packing FractionatingColumns, Ind. and Eng. Chem. Anal. Ed., vol. 8, No. 6 (1936), pp.451-45?

1. A STILL COMPRISING IN COMBINATION A CONDENSING SURFACE AND A TUBULAR,SMOOTH, HEATED EVAPORATION SURFACE SPACED FROM THE CONDENSING SURFACE,SAID EVAPORATION SURFACE HAVING TIGHTLY FITTED THEREON A READILYREMOVABLE, FLEXIBLE, PLIABLE, AND PERMEABLE COVERING SLEEVE OF INERT,ACID-RESISTANT, NON-METALLIC, MESH FABRIC OF MINERAL MATTER; TODISTRIBUTE THE DISTILLAND SUPPLIED TO THE HEATED EVAPORATION SURFACE ANDTO RETAIN SUBSTANTIALLY ALL TARRY AND GUMMY RESIDUE FORMED AT THEEVAPORATION SURFACE AND THUS PREVENT THE EVAPORATION SURFACE ITSELF FROMCOLLECTING THE SAID RESIDUE MATERIAL, AND MEANS TO SUPPLY DISTILLAND TOTHE HEATED EVAPORATION SURFACE.